A radar system operates by transmitting a high-intensity radio wave in a given direction. If the radio wave encounters a reflective object, part of the radio wave energy will echo or return to the antenna source and be detected by a receiver. By measuring the time to return, direction, and other signal characteristics of the echo, the radar system indicates the presence, distance, direction, velocity and other identifying features of the reflecting object.
Naval vessels typically maintain radar surveillance of nearby ships and aircraft during off-shore duty. The radar system provides information for navigation, station keeping of the convoy or battle group, control and recovery of aircraft, defensive and offensive surveillance, and direction and operation of on-board weapons systems. Because the radar systems are integrated to nearly every phase of the shipboard operations, a high level of maintenance is required to insure a high level of reliability. Routine maintenance includes periodic testing performed while the vessel is at sea and in port.
In-port testing of radar systems typically creates one notable difficulty. This difficulty involves the signal of the transmitting antenna. The high frequency, high power signal can interfere with other electronic equipment located at nearby on-shore facilities. This interference can be avoided by blocking transmission of the radar signal for a particular sector of rotation.
Examples of related radar systems which the Navy tests in-port include the AN/SPS-49 and the AN/SPS-40. Both the AN/SPS-49 and the AN/SPS-40 are two dimensional, air search radar systems which have an analog synchro voltage to indicate rotational bearing of the transmitting antenna. The AN/SPS-49, however, also has a sector-blanking system. The sector-blanking system includes a microprocessor of the radar system to generate a Radio Frequency (RF) gate to an RF amplifier of the SPS-49. This gate determines whether the RF amplifier will pass a signal for transmission by the antenna.
As with other radar systems, the signal transmitted by the AN/SPS-49 interferes with other electronic equipment during in-port testing. Adequate testing of the AN/SPS-49, however, may not require a full 360.degree. of transmission by the rotating antenna. Thus, a technician may determine which particular rotational region or sector the sensitive electronic equipment is located and adjust the sector-blanking system. The system then blocks transmission of the rotating antenna of the AN/SPS-49 for the predetermined sector and thereby prevents interference with other electronic equipment.
The sector-blanking system of the AN/SPS-49 is incompatible for the related AN/SPS-40 because the sector-blanking system utilizes the microprocessor of the SPS-49. The same microprocessor also operates the entire radar system. Accordingly, the sector-blanking system is integrated as part of the AN/SPS-49 system and cannot be readily disconnected and attached to other radar systems.
Another related art is U.S. Pat. No. 2,959,737 by Simopoulos. Simopoulos discloses a periodic signal selector and blanking generator for aircraft which prevents unwanted signals of any external circuitry from interfering with an indicating system. The blanking generator system includes a steady periodic signal selector, a gated input amplifier, a regenerating multivibrator, two blanking multivibrators, and a cathode follower.
During operation, an incoming trigger signal feeds into the gated input amplifier and into the steady periodic signal selector. When blanking of particular equipment from the indicating system is desired, a video trigger pulse is fed to the two multivibrators, which in turn generate a blanking output pulse. This pulse prevents the gated amplifier from amplifying the trigger input signal for a period of 35 to 100 microseconds. The length of the blanking signal depends on the number of spurious echoes generated by interfering equipment rather than on the rotational bearing of the antenna. Also, the system focuses on preventing external electronic equipment from affecting the system instead of preventing the system from affecting external equipment.